desktop-shell: Don't crash on zoom without a pointer in the seat

The zoom effect zooms at the seat's current pointer location.  When no
pointer is present the zoom key bindings cause a crash.

Instead, check for the absence of a pointer and log a warning.

Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
1 file changed